1. Field of the Invention
The present invention relates to plate heat exchanger and, more particularly, is concerned with a plate thereof having attachment holes and a seal thereof having nipples with cross sections different from the penetration cross section of the holes such that the nipples when inserted into the holes are not pressed about their entire circumference but only at spaced sites thereon at which the nipples project beyond the margin of the holes.
2. Description of the Prior Art
Before the plates of a plate heat exchanger are suspended in a frame and pressed together to form a packet, seals are fixed in grooves which facilitates handling the plates during the assembly. A known manner of fastening the seals is adhering the seals in grooves by use of an adhesive means which for the sealing effect itself is irrelevant but rather the adhesive means serves for the correct fixing of the position of the seals on the plates. This adhesion technique has some disadvantages. For example, before the application of the adhesive means, the grooves must be cleaned of, for example, oil and fat residues in order for the adhesive effect not to be impaired. Subsequently the adhesive means itself must be applied. All of this is rather time-consuming. Problems are also encountered in the maintenance of plate heat exchangers when a seal needs to be replaced. For this purpose the old seal must be removed and subsequently the groove must be cleaned of the adhesive means. An inspection of the groove bottom and the seal is also only possible, for example after the cleaning work on the dismounted heat exchanger, if the adhesion connection is previously destroyed.
Due to these disadvantages and the fact that in some technical fields, such as for example in medicine and food, adhesive means are to be avoided as much as possible, plate heat exchangers have been developed in which the seals are fastened mechanically, thus without adhesive means, on the plates. One feasibility known in the relevant technology for adhesive means-free seal fastening is that elastic nipples or projections, integrally developed with the seals, are brought into press fit with associated holes or openings in the plates.
According to patent document Nos. GB 2 071 303 A, GB 2 075 656 A and EP 0 134 155 A1, the nipples should have over-dimensions relative to the holes such that they can readily be pressed into the holes and can be pulled out again. It is therein to ensure that the seal is fixed securely at the intended site. This solution entails problems since the nipples as well as the seal as cast parts are subject to tolerance fluctuations. If the radial over-dimension of the nipples is too large, they can only be pressed into the holes with difficulty or not at all. If this is, nevertheless, successful, the nipples tear off when the seal is removed, for example during inspection or cleaning work, such that the seal must be replaced by a new seal.
The problem of tolerances in the radial nipple dimensions is solved through a plate heat exchanger disclosed in patent document No. EP 0 039 229 A2. Here, the nipples are provided on webs disposed laterally to the seal and developed integrally with it, from which the nipples project downwardly. Through the webs extends a pocket hole into the nipples. To fasten the seal, the nipples are positioned above the holes on the plates which are associated with the nipples. Subsequently a pin or like tool is introduced into the pocket hole and the nipples are then stretched by pressure onto the pin such that they become significantly thinner and can be placed into the holes without any problems. After the removal of the pin the nipples contract again to their original dimension whereby the ends of the nipples inserted through the holes expand to form a head covering the hole from below. The seals are consequently fastened securely on the plates. Of disadvantage in this technique is that tools are necessary to press the nipples in the holes. Furthermore, during inspection or maintenance work requiring the removal of the seals, the above-described consequences occur, the tearing off of the nipples.
Lastly, patent document No. EP 0 123 379 B1 discloses a plate heat exchanger in which the seal is fastened on the plate by means of elastic projections integrally developed with it, which extend into associated openings in the groove bottom. The openings are developed such that they comprise an insertion and pull-out region into which the projections can freely be moved, and from which they can be moved out again, along the margin of the openings without force. From this region the projections can be moved into a blocking region of the openings, in which the motion of the projections into the openings, respectively out of them again, is counteracted by strong resistance by compression between the projections and the margins of the openings, wherein moving the projections from the insertion and pull-out position into the blocked position, and conversely, is possible due to the elasticity (resiliency) of the seal.
Consequently, a need exists for an innovation in a plate heat exchanger of the type described above which will overcome the aforementioned problems without introducing new problems in place thereof.
The present invention overcomes the aforementioned problems in a plate heat exchanger by providing a simple solution for the mechanical fastening of the seals on the plates, which solution nevertheless permits a secure hold of the seals on the plates and also a problem-free removal of the seals from the plates. Specifically, each plate has attachment holes and each seal on a given plate has nipples projecting therefrom with cross-sections different from the penetration cross section of the holes such that the nipples when inserted into the holes are not pressed about their entire circumference but only at spaced sites thereon at which the nipples project beyond the margin of the holes. Since the cross-sections of the nipples are smaller than the penetration area of the holes, at other sites there is still clearance between the circumference of the nipples and the margin of the holes. Due to the elasticity of the nipples, their compressed material can expand into these free volumes, which leads to a decrease of the compression and consequently facilitates pressing the nipples into the holes. Through this displacement mechanism overtolerance in the radial dimensions of the nipples is extremely well compensated or, expressed differently, it is possible to work with relatively greater radial over-dimensions than is possible with the prior art.
Accordingly, the present invention is directed to a plate heat exchanger which comprises: (a) a plurality of adjoining plates disposed adjacent one another so as to form a packet, the plates having peripheral grooves and a plurality of channels alternately for media giving off heat and absorbing heat, and inlet and outlet openings for passage of the media through the channels between the adjoining plates; (b) a plurality of seals made of elastic material, each of the seals being emplaced between the adjoining plates in the groove of one of the adjoining plates; and (c) means for mechanically fastening each of the seals on one of the plates. The fastening means includes a plurality of attachment holes defined in each of the plates and a plurality of nipples made of elastic material and being insertable in the holes, the nipples being integrally formed on each of the seals at intervals spaced longitudinally along the seal, the nipples having cross sections different from penetration cross sections of the holes such that the nipples when inserted into the holes are not compressed about the entire circumference of the nipples but only at spaced sites thereon at which the nipples project beyond margins of the holes such that due to the elastic material the nipples can compress radially and axially so as to permit the pressing-in and pulling-out of the nipples into or out of the holes.
More particularly, the nipples have one of a polygonal and circular cross section and the holes have the other of the polygonal and circular cross section. The margins of the holes are provided as annular downturned edges pointing in the direction of insertion of the nipples into the holes. This forming of the holes has various advantages. Thus, for one, the contact area between nipple and hole is increased. Thereby, the radial over-dimension of the nipples required according to the prior art can be decreased while maintaining a secure hold of the seal. This permits the nipples to be pressed into and pulled out of the holes more readily. For another, the immersion of the nipples into the holes is facilitated since the ends of the nipples when they are inserted into the holes run against an encompassing radius on the margin of the holes. This radius also permits providing a radius at the transition from nipple to seal. This, for one, has advantages with respect to fabrication engineering during the production of the seal and, for another, it reduces the danger of the nipples being sheared off at this site during movements of the plates.
The tips of the nipples have truncated conical shapes which facilitates inserting the nipples into the holes. Preferably, each of the nipples has a trigonal cross-sectional configuration and each of the holes has a circular configuration. Further, each of the nipples has three edges circumferentially spaced apart and rounded off.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.